<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>半圆</title>
    <style>
        .semicircle{
            width: 100px;
            height: 200px;
            
            /*前四个值表示圆角的水平半径，后四个值表示圆角的垂直半径*/
            border-radius: 200% 0 0 200% / 100% 0 0 100% ;
            background-color: skyblue;
        }
    </style>
</head>
<body>
    <div class="semicircle"></div>
</body>
</html>